The long-term objectives of this project are 1) to systematically map the protein-protein interaction network mediated by modular domains (including their sequence specificity and in vivo interacting partners), 2) to understand the biological function of these interactions, and 3) to develop specific inhibitors against these domains as research tools and potential therapeutic agents. During this grant period, our studies will focus on 43 human Src homology 2 (SH2) domains. SH2 domains specifically function in protein tyrosine kinase pathways by binding to phosphotyrosyl (pY) proteins. SH2 domains perform a wide variety of functions and as such they are potential targets for therapeutic intervention of human diseases and conditions such as cancer, osteoporosis, allergy, asthma, and autoimmunity. The current grant period has the following specific aims. Specific Aim 1 is to determine the "high-resolution" sequence specificity for 20 or so SH2 domains that have been partially characterized by others and the structural basis for SH2 domains'ability to recognize multiple consensus sequences by a single binding site and their extended sequence specificity. Specific Aim 2 is to determine the sequence specificity for 23 new SH2 domains involved in JAK/STAT signaling pathways. Specific Aim 3 will employ a chemical/bioinformatic approach to identify the partner proteins for some of the SH2 domains. Finally in Specific Aim 4, linear and cyclic pY peptides and peptidyl aldehydes will be developed as specific SH2 domain inhibitors. The inhibitors will then be used to study the cellular function of the SH2 domain-containing proteins.